Linking response traits of novel seaweed communities to variation in environmental drivers across microhabitats of a tropical reef

Abstract The use of trait‐based ecology has improved prediction of community responses to global environmental challenges. However, one fundamental assumption, that variation in environmental drivers shapes distributions of community response traits, lacks the consistent and strong empirical links predicted by theory. Understanding the spatial scale at which environmental variation drives trade‐offs among ecological strategies, particularly across microhabitats, may help inform these links. Our objectives were to quantify functional trait distributions of seaweed communities across microhabitats of a tropical reef, relate community traits to ecological drivers that control seaweed performance and explore axes of variation that represent trade‐offs among ecological strategies. Our work is motivated by the emergence of novel seaweed communities with unknown functions after global losses of coral on tropical reefs. We created a typology linking traits to ecological processes and the environmental drivers that we hypothesized shape these trait distributions. We then measured environmental drivers (resource availability, herbivory pressure and physical disturbance) and response traits of seaweed communities in five microhabitats of a fringing reef. Environmental drivers varied among microhabitats, with herbivory and seaweed growth potential (a proxy for resources) decreasing with distance from shore, physical disturbance decreasing with water depth and light ranking highest in the shallowest microhabitats. Differences in community trait distributions among microhabitats reflected the relative strengths of these environmental drivers and uncovered two ecological strategies that maximized resource acquisition: one that resists herbivory and one that represents a ‘jack of all trades’. Synthesis . This research makes three novel contributions. First, we advance understanding of the scale of community trait variation by documenting substantial variation across microhabitats of a tropical reef. Second, we provide empirical support for the assumption that different combinations of environmental drivers shape unique community trait distributions. Third, we uncover four ecological strategies seaweed communities employ to maintain performance under different suites of environmental conditions. These findings broaden our overall understanding of community trait variation and provide a foundation for understanding shifts in community functioning on tropical reefs in response to human impacts. This is important as human impacts that drive these shifts will only intensify in the Anthropocene.